Geological Interpretations of Vertical Effective Stress-Compressional Sonic Transit Time Cross-plots for Pore Pressure Prediction

2019 ◽  
Author(s):  
D. Tassone
Keyword(s):  
Pore Pressure ◽  
Transit Time ◽  
Effective Stress ◽  
Pore Pressure Prediction ◽  
Vertical Effective Stress

Analysis of overpressure and its generating mechanisms in the northern Carnarvon Basin from drilling data

2012 ◽  
Vol 52 (1) ◽  
pp. 375
Author(s):  
Iko Sagala ◽  
Mark Tingay
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Late Triassic ◽  
Effective Stress Analysis ◽  
Pore Pressure Prediction ◽  
Pressure Indicators ◽  
Northern Carnarvon Basin ◽  
Vertical Effective Stress ◽  
Prediction Techniques ◽  
Carnarvon Basin

The Northern Carnarvon Basin is one of Australia’s most prolific hydrocarbon basins. Overpressure has been encountered in numerous wells drilled in the Northern Carnarvon Basin. Knowledge of overpressure distribution is important for drilling and exploration strategies, and understanding the origin of overpressure is essential for applying reliable pore pressure prediction techniques. Unconventional pore pressure indicators—primarily drilling kicks and the presence of connection gas—were used to improve an updated distribution of overpressure and to investigate the origin of overpressure in the Northern Carnarvon Basin. This unconventional dataset was compiled from 45 wells. Overpressures are observed in 40 wells and tend to occur near, or on, the Rankin Platform, Alpha Arch, and Barrow Trend. The presence of overpressure in this area coincides with the region of maximum Cenozoic deposition. Overpressured strata in the Northern Carnarvon Basin occurs through a wide stratigraphic range, from Late Triassic to Paleocene sequences. Generally, post Paleocene sequences in the Northern Carnarvon Basin are considered to be normally pressured. Porosity-vertical effective stress analysis in shale lithologies was used to investigate the origin of overpressure in the Northern Carnarvon Basin. Porosity-vertical effective stress plots from 28 wells in the Northern Carnarvon Basin identified 20 wells where the overpressure appears to be generated by disequilibrium compaction, and eight wells where the overpressure appears to be generated by a component of fluid expansion. Disequilibrium compaction mechanisms were the predominant cause of overpressure in wells around the Rankin Platform and areas located further away from the coast. Conversely, fluid expansion mechanisms were the predominant cause of overpressure in wells around the Alpha Arch and Bambra Trend, and an area located closer to the coast. These results broadly confirm those obtained from earlier studies and highlight the usefulness of kick and connection gas data in overpressure analysis.

Pore pressure prediction based on the Full Effective Stress (FES) method

2020 ◽  
Author(s):  
G. Richards ◽  
D. Roberts ◽  
A. Bere ◽  
S. Martinez ◽  
M. Tilita ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Pore Pressure Prediction

scholarly journals Pore Pressure Prediction using Well-Logging Data in the West Baram Delta, Offshore Sarawak Basin, Malaysia

2019 ◽  
Vol 8 (4) ◽  
pp. 9172-9178
Keyword(s):  
Pore Pressure ◽  
Transit Time ◽  
Oil Recovery ◽  
Oil And Gas ◽  
Gamma Ray ◽  
Reservoir Modeling ◽  
Gas Field ◽  
Overburden Pressure ◽  
Trend Line ◽  
Pore Pressure Prediction

Well-predicted pore pressure is vital throughout the lifetime of an oil and gas field starting from exploration to the production stage. Here, we studied a mature field where enhanced oil recovery is of high interest and pore pressure data is crucial. Moreover, the top of the overpressure zone in west Baram Delta starts at different depths. Hence, valid pore pressure prediction prior to drilling is a prerequisite for reducing drilling risks, increasing efficient reservoir modeling and optimizing costs. Petrophysical logs such as gamma-ray, density logs, and sonic transit time were used for pore pressure prediction in the studied field. Density logs were used to predict the overburden pressure, whereas sonic transit time, and gamma-ray logs were utilized to develop observed shale compaction trend line (OSCTL) and to establish a normal compaction trend line (NCTL). Pore pressure was predicted from a locally observed shale compaction trend line of 6 wells using Eaton’s and Miller's methods. The predicted pore pressure using Eaton’s DT method with Eaton’s exponent 3 showed a better matching with the measured pressure acquired from the repeat formation test (RFT). Hence, Eaton’s DT method with Eaton exponent 3 could be applied to predict pore pressure for drilling sites in the study area and vicinity fields with similar geological settings.

An Analytical Solution for Wave-Induced Soil Response and Seabed Liquefaction

2010 ◽  
Author(s):  
Xiang-Lian Zhou ◽  
Jian-Hua Wang ◽  
Yun-Feng Xu
Keyword(s):  
Shear Modulus ◽  
Pore Pressure ◽  
Effective Stress ◽  
Fourier Transformation ◽  
Saturated Porous Medium ◽  
Helmholtz Equations ◽  
Soil Response ◽  
Depth Increase ◽  
Vertical Effective Stress ◽  
Wave Induced

In this study, an analytical method to solve the wave-induced pore pressure and effective stress in a saturated porous seabed is proposed. The seabed is considered as a saturated porous medium and characterized by Biot’s theory. The displacements of the solid skeleton and pore pressure are expressed in terms of two scalar potentials and one vector potential. Then, the Biot’s dynamic equations can be solved by using the Fourier transformation and reducing to Helmholtz equations that the potentials satisfy. The general solutions for the potentials are derived through the Fourier transformation with respect to the horizontal coordinate. Numerical results show that the permeability and shear modulus of the porous seabed has obvious influence on the response of the seabed. The vertical effective stress and attenuation velocity of pore pressure along seabed depth increase as permeability k increases. The liquefaction may be occur at the surface of seabed when shear modulus decreasing.

Pore-pressure prediction challenges in chemical compaction regimes: An alternative VP/VS-based approach

2016 ◽  
Vol 4 (4) ◽  
pp. T443-T454 ◽  
Author(s):  
Ajesh John
Keyword(s):  
High Temperature ◽  
Pore Pressure ◽  
Effective Stress ◽  
Text Analysis ◽  
Correction Coefficient ◽  
S Wave ◽  
Wave Velocities ◽  
Temperature Regimes ◽  
Pore Pressure Prediction ◽  
High Degree

Understanding pressure mechanisms and their role in porosity-effective stress relationship is crucial in pore-pressure prediction estimation, particularly in complex geologic and high-temperature regimes. Overpressures are commonly associated with undercompaction and/or unloading mechanisms; those associated with undercompaction generally possess a direct relationship between effective stress and porosity, whereas those associated with unloading do not provide such direct indications from porosity trends. The type of associated unloading mechanism can be correlated when the effective stress and velocity become distorted with the onset of unloading. In the Ravva field, the pore-pressure distribution and overpressure mechanism in the Miocene and below it is a classic example of the unloading mechanism related to chemical compaction, thereby making it difficult to resolve the magnitude and trend of pore pressures. Here, the ratio of P- and S-wave velocities ([Formula: see text]) is analyzed from the drilled locations to understand the effects of lithology, pressure, and fluids on formation velocities and indicates a distinct decreasing trend across the overpressure formations, which I have corresponded to excess pressure resulting from chemical compaction. Across the high-pressured zones, [Formula: see text] ratios show low values compared with normally pressured zones possibly due to the presence of hydrocarbon and/or overpressures. A velocity correction coefficient ranging 0.83–0.71 is resolved for overpressure zones by normalizing the [Formula: see text] values across the normally pressured formations, and thereby assuring that a pore-pressure estimation using corrected velocity from [Formula: see text] analysis shows a high degree of accuracy on prediction trends. Pore-pressure predictions based on [Formula: see text] are a more effective and valid approach in high-temperature settings, in which numerous factors can contribute to pressure generation and a direct effective stress-porosity relationship deviates from the trend.

scholarly journals Chemical compaction of deep buried mudstone and its influence on pressure prediction

2020 ◽  
Vol 600 (1) ◽  
pp. 012012
Author(s):  
Li Chao ◽  
Luo Xiaorong ◽  
Zhang Likuan ◽  
Lei Yuhong ◽  
Chen Ming ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Clay Minerals ◽  
Eastern China ◽  
Bohai Bay ◽  
Dongying Depression ◽  
Pore Pressure Prediction ◽  
Shahejie Formation ◽  
Vertical Effective Stress ◽  
The Impact ◽  
Transformation Of Clay Minerals

Abstract The chemical compaction of mudstones which is dominated by the transformation of clay minerals leads to significant changes in the mineral composition and microstructure of mudstone during process of deep burial. In particular, the transformation of smectite to illite in mudstones results in noticeable impact on the pore pressure formation and the overpressure logging responses. At present, the study about the pressurization mechanism of chemical compaction and the impact on overpressure logging responses is really weak, which made it hard to pore pressure identification and pressure prediction for deep buried formations. Taking the Paleogene Shahejie Formation in the Dongying depression of the Bohai Bay Basin in eastern China as typical case, this paper analyses the characteristics of clay mineral transformation of the Shahejie Formation in the Dongying depression, the logging responses of overpressures, and the influence of chemical compaction on the prediction of pore pressure. The results showed that the chemical compaction of mudstones changes the relationship between the petrophysical properties of mudstone and vertical effective stress and the logging responses of overpressure. The typical characteristic of chemical compaction manifested as density increase continuous with the depth. The normal compaction trends of the different compaction stages are the basis for overpressure mechanisms identification and pore pressure prediction. The depth of the rapid transformation of clay minerals has a good consistency with the top of overpressure zone (2000–2800 m) in Dongying depression, which indicates that the overpressure and its logging responses may be related to the chemical compaction of mudstones. The measured pressure in intervals deeper than 3000 m is closer to the predicted pressure based on the normal compaction trend of chemical compaction.

Reducing the variation of Eaton’s exponent for overpressure prediction in a basin affected by multiple overpressure mechanisms

2014 ◽  
Vol 2 (1) ◽  
pp. SB57-SB68 ◽  
Author(s):  
K. Suwannasri ◽  
W. Promrak ◽  
S. Utitsan ◽  
V. Chaisomboonpan ◽  
R. J. Groot ◽  
...  
Keyword(s):  
Spatial Variation ◽  
Pore Pressure ◽  
Work Practice ◽  
Potential Method ◽  
Pressure Measurements ◽  
Data Set ◽  
Pore Pressure Prediction ◽  
Vertical Effective Stress ◽  
Well Data ◽  
Global Parameters

Deriving global parameters for velocity-based pore pressure predictions in a complex overpressure origins regime is normally difficult and nonrobust. Applying large variations in Eaton’s exponent is an unsatisfactory work practice for velocity-based pore pressure prediction. This study investigates an alternative potential method to reduce the variation of Eaton’s exponent values in an environment of mixed disequilibrium compaction and fluid expansion overpressure mechanisms. Using 25 input wells, the fluid expansion components are estimated using velocity-vertical effective stress plot and then subtracted from the pressure measurements to obtain the disequilibrium compaction components. Eaton’s exponents are then derived only from the disequilibrium compaction components. The spatial variation of Eaton’s exponent is greatly reduced from the range of 1–5 to the range of 1–1.9 after removing the fluid expansion components from the raw overpressure data set. A constant Eaton’s exponent of 1.44 is used throughout the field to predict the disequilibrium compaction components and the fluid expansion components are predicted from gridding of the well data. The two components are combined to produce a final pore pressure prediction profile, which yields less uncertainty than the traditional Bowers method.

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